1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer and a facsimile apparatus employing the electrophotographic method, and particularly, relates to an image forming apparatus that cools down a sheet heated by a fixing portion.
2. Description of the Prior Art
In an electronic copying image forming apparatus, a toner image formed on a photoreceptor is transferred onto a sheet at a transfer portion. The sheet onto which the toner image is transferred is sent to the fixing portion, to which heat and pressure is applied at the fixing portion, and the toner image is thereby fixed on the sheet. Thereafter, the sheet is discharged to a paper output tray from a discharge portion and stacked on the paper output tray.
However, when the sheet is discharged as it is without being cooled down, the sheet stacked on the paper output tray is not sufficiently cooled down so that a phenomenon has occurred such that the surfaces of the sheets stacked on the paper output tray that lie next to each other are adhered by toner due to a high temperature (hereinafter, such a phenomenon is referred to as a sticking phenomenon). The sticking phenomenon has notably occurred at the time of duplex printing, at the time of high-speed printing and at the time of printing that uses a low-melting-point toner.
For reducing such a sticking phenomenon, it is considered that a feed path length from the fixing portion to the paper output tray is extended to gain a cooling time, however, miniaturization of an image forming apparatus has been advanced as seen in recent years, and it has been thus impossible to employ this method.
Consequently, when a sheet after passing through the fixing portion is conveyed by a pair of feed rollers in a feed path, cooling down of the sheet is performed by blowing air.
However, in image forming apparatuses that are described in Patent Literature 1 (Japanese Patent Application Laid-open Hei 8 No. 171338) and Patent Literature 2 (Japanese Patent Application Laid-open No. 2006-106668), an air blowing timing and an air volume for the sheet in the feed path are not considered. Hence, an influence on conveying performance of the sheet such as curing up of a tip end of the sheet, bending and tearing up of the sheet due to the tip end of the sheet not being appropriately put into a nip of the pair of the rollers, and a paper jam, by blowing air to the sheet, is not considered.